This invention concerns a new method for the formation of abundant quantities of Aluminum Nitride (AlN) from a thermal treatment of a mixture of aluminum oxide (Al2O3) and shells of almond, cashew, coconuts, pistachio, and walnuts in a nitrogen atmosphere at temperatures in excess of 1450° C.
This new method of synthesizing Aluminum Nitride from various Nut Shells uses conventional heating or microwave heating to produce nano-structures.
Billions of pounds of agricultural waste of nut shells such as those of almonds, pistachios, walnuts, cashew, coconuts, macadamia etc. are generated every year all over the world.
Aluminum Nitride (AlN) is a very useful material for industrial and electronic applications due to its unique physical properties.
AlN is an insulator in electronic device applications because of high electrical resistivity, low thermal expansion, resistance to erosion and corrosion, excellent thermal shock resistance and chemical stability in air up to 1380° C. with surface oxidation occurring at 780° C.
Surface acoustic wave sensors (SAWs) can be deposited on silicon wafers because of AlN's piezoelectric properties and AlN can be used as an RF filter for mobile phones.
AlN is synthesized in the bulk form by the carbothermal reduction of aluminum oxide in the presence of gaseous nitrogen or ammonia or by direct nitridation of aluminum. In order to get a fully dense form, Y2O3 or CaO are required as additives during the hot pressing.
Aluminum nitride is a wide gap semiconductor with band gap between 6.01-6.05 eV at room temperature. It crystallizes in wurtzite phase and has many potential applications in microelectronics due to its relatively high thermal conductivity (70-210 W·m−1·K−1 to 285 W·m−1·K−1). In addition, other unique properties that make it an attractive for applications include high electrical resistivity, low thermal expansion, resistance to erosion and corrosion, excellent thermal shock resistance and chemical stability in air up to 1380° C. with surface oxidation occurring at 780° C.
Epitaxially grown thin film crystalline aluminum nitride is used for surface acoustic wave sensors (SAWs) deposited on silicon wafers because of AlN's piezoelectric properties. Another important application for AlN is its application as an RF filter which is widely used in mobile phones, which is also called a thin film bulk acoustic resonator (FBAR). AlN is synthesized in the bulk form by the carbothermal reduction of aluminum oxide in the presence of gaseous nitrogen or ammonia or by direct nitridation of aluminum. In order to get fully dense form, Y2O3 or CaO are required as additives during the hot pressing.
Among the agriculture waste products, there are two types, one containing silica and carbonaceous matter and the other one contains mostly carbonaceous matter and no silica. The first kind includes rice husk, wheat husk, and peanut shells. We have demonstrated that they can be utilized to produce industrially important materials such as SiO2, SiC, Si3N4, and zinc silicate by pyrolyzing them in air, argon or in nitrogen atmospheres.
The second kind of agriculture residues are nut shells which contain only carbonaceous matter such as almond, walnuts, pistachio, coconuts, macadamia, cashew, etc. Billions of pounds of nut shells are produced annually all over the world and will be available if they can be harnessed in the synthesis of industrially important materials. Recently, it was reported that mixed phases of SiC and Si3N4 can be produced by carbothermal reduction and nitridation of a mixture of silica and macadamia powder.
We have demonstrated in our recent work that by adding ZnO to powder of wheat or rice husk, pure zinc silicate can be produced with photo-luminescent properties.
Here, we have developed the formation of AlN from the nut shells powder by adding nanocrystalline powders of Al2O3 to the nut shells powder of almond, walnut, coconut, macadamia, pistachio and cashew and pyrolising them in nitrogen atmosphere at 1400 to 1500° C.
Energy dispersive X-ray fluorescence technique was used to determine the elemental composition of the nuts with very slight variation among them. The formation of pure wurtzite phase of AlN was confirmed by x-ray diffraction and Rietveld analysis and Raman spectroscopy. Transmission electron microscopy was used to confirm the nanocrystallinity of AlN and to characterize the size distribution.